1. Technical Field
An aspect of the present invention relates to a sensor for measuring water fraction in a fluid mixture, and more particularly, but not by way of limitation, to a fluid mixture flowing in a borehole of a hydrocarbon well.
2. Background Art
At various moments in the lifetime of a hydrocarbon well, it is important to identify downhole reservoir zones, and in particular the fraction of water produced relative to the hydrocarbon fluid (e.g., oil, gas). Water production and disposal from hydrocarbon fluid production are costly operations and may be have ecological drawbacks. Thus, early identification enables taking quick appropriate remedial action.
During drilling operations and shortly after a hydrocarbon well has been drilled, the water fraction in the fluid mixture flowing from the geological formation into the borehole may be measured, for example, by running a wireline sonde. This enables identifying zones that produce excessive water. After completion operations and after production operations have begun, making water fraction measurements by running a wireline sonde is prohibitively expensive or technically impractical due to the presence of completion/production equipments like packers, production tubings, etc. Further, hydrocarbon wells equipped with a sub-sea well head or having a long horizontal producing section cannot be logged in a conventional or cost effective manner.
It is known to deploy permanent sensors for measuring oil and water fraction at the reservoir level. Measuring tools may be deployed into a well to form an array. However, this has not been commercially viable due to the complexity of the tools and the high capital investment.
Furthermore, it is known in the art to measure water fraction in a fluid mixture flowing into a conductive pipe by measuring the capacitance between two plates or electrodes in direct contact with the fluid mixture. The two plates are manufactured as thin layers of metal and are electrically insulated from the conductive pipe. In harsh downhole environment encountered in the oilfield industry, the conductive pipe is made of steel or other metal alloy in order to resist the surrounding wellbore pressure and chemical aggression. It is difficult to maintain the electrodes on the inner face of the conductive pipe and electrically insulate each electrode from the pipe. In particular, the insulation cannot withstand downhole conditions over a long period of time.